1. Field of the Invention
The present invention relates to the shaping of glass sheets. More particularly, though not exclusively, the present invention relates to the shaping of glass while at least a portion of the glass sheet is supported on a bed of hot gas and lifted with an outline portion thereof supported on an outline lifting member into conformity with a vacuum holder of complementary shape to that of the outline lifting member. In a specific embodiment of the present invention, the vacuum holder comprises a vacuum chamber with a downward facing wall that is apertured for applying suction to the vacuum chamber communicating with the apertures through the downward facing wall of the upper shaping mold. The wall has a main portion that is substantially flat or gently curved and one or more end portions that are more sharply bent relative to the main portion.
In the past, a gas hearth bed supported the glass sheet for conveyance into the shaping station. The glass sheet, on arrival at the gas hearth bed portion within the shaping station, was lifted on an outline lifting member into conformity with a vacuum holder. When the gas hearth bed portion was larger than the sheet to be shaped, it had to be provided with a continuous recess within its outline for receiving the outline lifting member. When the gas hearth portion had an outline slightly smaller than the glass sheets being shaped, the outline lifting member, when lowered, surrounded the gas hearth bed portion within the shaping station. In either case, it was necessary to provide a unique gas hearth bed portion having either an outline shape or a grooved portion that conformed to the outline of the glass sheet supported thereon. Prior attempts to provide a gas hearth bed portion of rectangular outline small enough to accommodate all sizes of glass sheets to be bent was impractical, because the overhanging portions of the flat glass sheet that were bent relative to the main body portion tended to sag uncontrollably in their unsupported regions until the lifting member engaged the glass sheet to lift the glass sheet from its position of alignment with respect to the gas hearth bed portion to a position of engagement with the vacuum holder, particularly with glass sheets of larger extent than the gas hearth portion in the shaping station.
Vacuum holders moved vertically relative to the flat glass sheet to suck up the glass against the flat portion of the vacuum holder, which then lifted the glass sheet held by suction thereagainst until a gap of sufficient size developed to permit introducing a shaping member such as a tempering ring between the vacuum holder and the gas hearth portion. The glass sheet was shaped by drop forming the sheet released from the vacuum holder onto the tempering ring. Initially, the shape that could result was limited in its applicability to relatively flat sheets. Recently, however, more complicated bends have been required of the glass which required the use of auxiliary lifting members to engage the opposite end portions of the glass sheet to bring the heat-softened glass into engagement with the curved end portions of a vacuum holder. In the past, the extending end portions were free to sag during the time beginning when the glass sheet arrived in position at the shaping station, and ending with the lifting of the glass sheet. The latter lifting did not necessarily compensate for the sagging that occurred during the interval when the glass sheet waited to be lifted above the position of support provided by the gas hearth bed portion.
The prior art failed to provide a solution to the problem of avoiding excessive sag of the extended portions of the glass sheet without requiring the substitution of a gas hearth portion of conforming outline shape or having an outline groove of requisite shape every time there was a change in the pattern being produced. Such a change was both expensive and time consuming.
2. Description of Patents of Interest
U.S. Pat. No. 3,468,645 to McMaster et al discloses a glass bending operation in which a flat glass sheet is supported by hot gas and delivered onto a gas hearth portion where it is lifted by a frame-like member adapted for movement between a recessed portion within a continuous groove in the gas hearth portion and an upward position in mating relation with an upper shaping member, which may be a vacuum-type mold. This apparatus requires the replacement of the gas hearth portion with one having a continuous groove conforming to approximately the outline shape of a different glass sheet required to be bent every time the production pattern changes.
U.S. Pat. Nos. 3,682,613 to Johnson et al and 3,846,104 to Seymour each disclose a ring-like mold in surrounding relation to the gas hearth portion. Thus, if the gas hearth extension were provided with small enough rectangular outline to permit the handling of a wide variety of glass sheet sizes, the ring-like mold adapted to engage and lift larger parts in surrounding relation to the gas hearth portion had to be spaced a considerable distance from the perimeter of the gas hearth portion to engage larger sheets near their margin. This would provide a space therebetween for glass sheets having larger dimensions than the gas hearth extension that would permit uncontrolled sagging. Otherwise, the gas hearth bed portion has to be replaced by a portion of a size sufficient to fit within the lifting mold.
U.S. Pat. No. 4,229,200 to Seymour shows a lifting frame 126 with a curved shaping rail 124 at each end. The lifting frame surrounds a hearth block or gas hearth bed portion in its lower position in combination with a vertically moving vacuum holder that moves downward in position to engage the center portion of a flat glass sheet and to have the curved shaping rails 124 lift the glass against a corresponding curved end portion of an upper vacuum holder. The vacuum holder supports the glass by vacuum and improves its shape by continuing to apply the vacuum when the lifting mold 126 is lowered and the vacuum holder raised to permit the entry of a shaping mold 128 on a shuttle 61. The vacuum holder releases the glass sheet shaped thereagainst to permit the glass sheet to fall and to be shaped by drop forming the sheet by impact onto the shaping mold 128 into the shape corresponding to that of the shaping mold 128. The latter then moves the shaped glass sheet into position between upper and lower nozzles which cool the glass.
In this patent, also, since the glass sheet is shaped to a relatively sharp bend at each end, the flat glass sheet extends a considerable distance beyond the ends of the gas hearth portion 125 so the glass is not prevented from sagging in its unsupported end portions during a critical time just before the curved shaping rails 124 engage and lift the glass into conformity with the vacuum mold.
This invention has found a way to support one or more end portions that extends beyond the outline of the gas hearth bed portion to avoid the uncontrolled sagging or the need for substituting gas hearth portions conforming to different outline patterns in many cases where changes in pattern are required to meet customer requirements.